Optical module and method for manufacturing the same

ABSTRACT

According to embodiments, a method for manufacturing an optical module may include: applying a polyamic acid solution to an upper surface of a substrate structure to form an adhesive layer; forming an active functional group on an upper surface of the adhesive layer; applying a polyamic acid solution to a first surface of a prism to form a prism adhesive layer; forming a polyamic acid layer on at least one of a planarized upper surface of the adhesive layer and a lower surface of the prism adhesive layer; disposing the prism on the substrate structure such that the polyamic acid layer contacts the adhesive layer and the prism adhesive layer; and applying pressure to the prism and the substrate structure to bond the adhesive layer to the prism adhesive layer.

BACKGROUND

The present disclosure herein relates to an adhesive structure and amethod for manufacturing the same, and more particularly, to an opticalmodule formed using an adhesive structure including a refractiveindex-matching adhesive layer.

A refractive index-matching oil is used for an optical module to measurean optical phenomenon. A material used for an optical module is requiredto have durability and strength at a high temperature. However, anadhesive or an adhesive film other than oil may not be suitable for anoptical module due to their low refractive index. Also, an issue israised that the adhesive or adhesive film exhibits a decrease instrength at a high temperature.

In the 1960s, Dupont developed a thermosetting polyimide. Afterwards,Dupont, NASA, and Mitsui Toatsu Chemicals developed a thermoplasticpolyimide. Polyimide, however, is generally non-transparent, and thushas a limitation in application to an optical device or an opticalpackage.

SUMMARY

The present disclosure provides a method for forming an adhesivestructure by using an adhesive layer with improved adhesive strength andhigh transparency.

The present disclosure also provides an adhesive structure with lessoptical signal loss and a method for manufacturing the same.

The present disclosure relates to an optical module and a method formanufacturing the same. A method for manufacturing an optical structureaccording to the inventive concept include: preparing a substratestructure; applying a polyamic acid solution to an upper surface of thesubstrate structure to form an adhesive layer; planarizing the adhesivelayer to form an active functional group on an upper surface of theadhesive layer; applying a polyamic acid solution to a first surface ofa prism to form a prism adhesive layer; forming a polyamic acid layer onat least one of the planarized upper surface of the adhesive layer and alower surface of the prism adhesive layer wherein the polyamic acidlayer is in a liquid state; disposing the prism on the substratestructure such that the polyamic acid layer contacts the adhesive layerand the prism adhesive layer, and applying pressure to the prism and thesubstrate structure to bond the adhesive layer to the prism adhesivelayer.

In an embodiment, the applying of pressure to the prism and thesubstrate structure may be performed at a temperature lower than acuring temperature of the polyamic acid layer.

In an embodiment, the applying of pressure to the prism and thesubstrate structure may be performed at a temperature ranging from 80°C. to 150° C.

In an embodiment, the prism adhesive layer may include the samepolyimide as the adhesive layer.

In an embodiment, the polyamic acid layer may include the same materialas the polyamic acid solution.

In an embodiment, the bonding of the adhesive layer to the prismadhesive layer may include forming intermolecular van der Waals force,an electric dipole bond or an induced dipole bond between a polyamicacid included in the polyamic acid layer and the active functionalgroup.

In an embodiment, the active functional group may include a danglingbond.

In an embodiment, the bonding of the adhesive layer to the prismadhesive layer may include forming an ionic bond, a covalent bond or ametallic bond between a polyamic acid included in the polyamic acidlayer and the active functional group.

In an embodiment, the bonding of the adhesive layer to the prismadhesive layer may include infiltrating a polyamic acid included in thepolyamic acid layer into the adhesive layer or the prism adhesive layer,and solidifying the infiltrated polyamic acid.

In an embodiment, the substrate structure may include an opticalwaveguide, the optical waveguide may have a refractive index of 1.5 to20, the adhesive structure may have a refractive index of 1.55 to 2.0,and the prism may have a greater refractive index than the opticalwaveguide.

In an embodiment, the forming of the adhesive layer may include:

spin-coating the polyamic acid solution on a surface of the substratestructure to form a first preliminary adhesive layer; conducting curingon a surface of the first preliminary adhesive layer to form a firstadhesive layer; and the first adhesive layer may include a polyimide.

In an embodiment, the forming of the adhesive layer may include:

forming a second preliminary adhesive layer on the first adhesive layer;and carrying out curing on a surface of the second preliminary adhesivelayer to form the second adhesive layer, wherein the second preliminaryadhesive layer may include a polyamic acid, and the second adhesivelayer may include a polyimide.

In an embodiment, the preparing of the substrate structure may includestacking a lower clad layer, an optical waveguide, and an upper cladlayer on a substrate.

In other embodiments of the inventive concept, an optical moduleincludes: a substrate structure including a substrate, a lower cladlayer, an optical waveguide layer, and an upper clad layer which arestacked; a prism having a first surface and an inclined surface; and anadhesive structure provided between the substrate structure and thefirst surface of the prism and having a refractive index of 1.55 to2.00, wherein the adhesive structure includes: an adhesive layerprovided on the optical waveguide and the upper surface of the cladlayer and having a polyimide; and a prism adhesive layer provided on thefirst surface of the prism and containing the same polyimide as theadhesive layer, wherein at least one of a chemical bond andintermolecular interaction is formed between the adhesive layer and theprism adhesive layer.

In an embodiment, the polyimide may include at least one amongtrifluoromethyl (—CF₃), sulfone (—SO₂) and/or ether (—O—) groups.

In an embodiment, the optical waveguide layer may have a refractiveindex of 1.5 to 2.0 and the prism has a greater refractive index thanthe optical waveguide layer.

In an embodiment, the adhesive structure may include a polymerizationunit derived from an aromatic dianhydride monomer and a polymerizationunit derived from a monomer including diamine group.

In an embodiment, transmittance of 500 nm to 2000 nm light to theadhesive structure with a thickness of 1 μm may be 95% to 100%.

In an embodiment, the intermolecular interaction may include van derWaals force, an electric dipole bond, or an induced dipole bond, and thechemical bond includes an ionic bond, a covalent bond or a metallicbond.

In an embodiment, voids and bubbles may not be formed between theadhesive layer and the prism adhesive layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the inventive concept, and are incorporated in andconstitute a part of this specification. The drawings illustrateexemplary embodiments of the inventive concept and, together with thedescription, serve to explain principles of the inventive concept. Inthe drawings:

FIGS. 1 through 11 are a flowchart showing a method for manufacturing anoptical module according to an embodiment;

FIG. 12 is a flowchart showing a method for preparing an adhesivestructure and an optical module according to other embodiments;

FIG. 13A is a cross-sectional view of an optical module according toother embodiments; and

FIG. 13B is an enlarged view of area A shown in FIG. 13A.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the inventive concept will be described belowin more detail with reference to the accompanying drawings for asufficient understanding of the configuration and effect of theinventive concept. The inventive concept, however, should not beconstrued as limited to the embodiments set forth herein. Rather, theinventive concept may be embodied in different forms and variouslymodified. These embodiments are given to provide complete disclosure ofthe inventive concept and to fully convey the scope of the inventiveconcept to those skilled in the art. Those skilled in the art willappreciate that the inventive concept may be carried out in a certainsuitable environment.

Terms used in the specification are only for explaining embodiments, notfor limiting the inventive concept. The terms of a singular form includeplural forms unless referred to the contrary. As used herein, the termsof a singular form may include plural forms unless the context clearlyindicates otherwise. It will be further understood that the terms“include,” “comprises” and/or “including,” “comprising,” when used inthis specification, specify the presence of stated features, steps,operations, and/or elements, but do not preclude the presence oraddition of one or more other features, steps, operations, and/orelements.

In the specification, when a film (or layer) is referred to as being onanother film (or layer) or substrate, it may be directly on the otherfilm or substrate, or intervening a third film (or layer) may bepresent.

Although the terms such as first, second, third, etc. are used herein todescribe various regions, films (or layers) and the like, these regions,films (or layers), and the like should not be limited by these terms.These terms are used only to distinguish one region or film (or layer)from another region or film (or layer). Therefore, a film materialreferred to as a first film material in one embodiment may be referredto as a second film material in another embodiment. An embodimentdescribed and exemplified herein includes a complementary embodimentthereof.

Unless otherwise defined, the terms used in embodiments of the inventiveconcept may be interpreted as meaning commonly known to those skilled inthe art.

In the chemical formula of the specification, unless a specificdefinition is otherwise provided, a hydrogen atom is bonded at theposition when a chemical bond is not drawn where supposed to be given.

Like reference numerals refer to like elements throughout.

Hereinafter, an adhesive and a method for manufacturing the sameaccording to embodiments will be described.

An adhesive according to the inventive concept may be an adhesivematerial and/or an adhesive composition. The adhesive may be used toform an adhesive layer which will be described later. The adhesive mayhave a relatively high glass transition temperature. The adhesive mayhave a refractive index of about 1.55 to about 2.0. The adhesive mayhave solvent resistance. The solvent resistance may refer to lowreactivity or no reactivity with a solvent. The solvent, for example,may include acetone and/or methanol. Accordingly, the adhesive may bereadily applied to a process for manufacturing a semiconductor device,an optical device, and an optical module. For instance, the adhesive maynot be damaged by the solvent during the cleaning process for asemiconductor device, an optical device and an optical module. Theadhesive may have a high transmittance. A film with a thickness of 1 μmprepared using the adhesive layer may have a transmittance of 95 to 100%for 500 to 2000 nm light. A film with a thickness of 100 μm preparedusing the adhesive may have a transmittance of 90 to 100% for 500 to2000 nm light.

The adhesive may include a polyamic acid and/or derivatives thereof. Thepolyamic acid and derivatives thereof may include an aromatic ring. Thearomatic ring may include, for example, a benzene or cycloolefinstructure. The polyamic acid and derivatives thereof may include a highelectronegative element or a high electronegative group. The highelectronegative element/group may be included in the main chain of theadhesive. The high electronegative element/group may include at leastone among trifluoromethyl (—CF₃), sulfone (—SO₂) and/or ether (—O—)groups. Accordingly, a polyimide prepared using the polyamic acid mayhave a high transmittance for a certain wavelength. Hereinafter, thespecification defines that a polyamic acid includes a polyamic acid andderivatives thereof. A polyimide is defined as one having a polyimideand derivatives thereof.

The polyamic acid according to embodiments may include a polymerizationunit derived from an aromatic dianhydride monomer and a polymerizationunit derived from a monomer including a diamine group. Thepolymerization unit derived from a monomer including a diamine group maybe bonded to the polymerization unit derived from an aromaticdianhydride monomer. At least one of the aromatic dianhydride monomerand the monomer including a diamine group may include a highelectronegative element/group. The dianhydride monomer may include ODPA(4,4′-Oxydiphthalic anhydride), PMDA (Pyromellitic dianhydride), DSDA(3,3′,4,4′-Diphenylsulfone tetracarboxylic dianhydride), BPDA(3,3′,4,4′-Biphenyltetracarboxylic dianhydride), BPADA (4,4′-Bisphenol Adianhydride), 6FDA (2,2′-Bis-(3,4-Dicarboxyphenyl) hexafluoropropanedianhydride), BTDA (3,3′,4,4′-Benzophenone tetracarboxylic dianhydride),CHDA (1,4-Cyclohexanedicarboxylic acid) and/or derivatives thereof. Thearomatic dianhydride monomer, for example, may include at least one ofthe materials shown in formula 1 below.

The monomer including a diamine group, for example, may include, TFB(2,2′-Bis(trifluoromethyl)benzidine), m-XDA (m-Xylylenediamine),3,4′-ODA (3,4′-Oxydianiline), 4,4′-ODA (4,4′-Oxydianiline), m-BAPS(2,2-Bis [4-(3-aminophenoxy) benzene], BAPB (4,4′-Bis (4-aminophenoxy)biphenyl), BAPP (2,2-Bis [4-(4-aminophenoxy)phenyl] propane) and/orderivatives thereof. The monomer including a diamine group may includeat least one of the materials shown in formula 2 below.

Producing the adhesive layer may include preparing an adhesive includinga polyamic acid (PAA) and synthesizing a polyimide by an imidizationprocess of the polyamic acid.

The polyamic acid may be prepared by the reaction of an aromaticdianhydride monomer and a monomer including a diamine group. Forexample, the aromatic dianhydride monomer and the monomer including adiamine group are added to a first solvent to prepare a reactionsolution. The first solvent, for instance, may include DMAc(N,N-dimethylacetamide), DMF (dimethylforamide), NMP(N-methyl-1-2-pyrollidone), and/or m-cresol. The reaction solution isreacted under a nitrogen atmosphere for 5 to 24 hours to prepare apolyamic acid solution. The polyamic acid solution, for example, mayinclude 10-30 wt % of an intermediate product and 70-90 wt % of aresidual solvent. The intermediate product is a solid material dissolvedin the residual solvent and may be an extract resulted from reaction.The intermediate product may include a polyamic acid. The residualsolvent may include the same material as the first solvent.

The polyamic acid imidization process according to an embodiment may beperformed by a thermal imidization process. The thermal imidizationprocess may include heating the polyamic acid at 200° C. to 350° C. Thepolyamic acid may include a plurality of polyamic acid molecules. Anintermolecular bonding between the polyamic acid molecules may be formedby the imidization process, resulting in vitrification of the polyamicacid. A chain structure among a plurality of polyamic acid molecules maybe formed by the intermolecular bonding. Subsequently, a polyimide isprepared. At least some of the residual solvent may be evaporated duringthe thermal imidization process. For example, volatile materials andwater in the residual solvent may be evaporated.

When the polyamic acid is heated at a temperature lower than glasstransition temperature (Tg), the polyamic acid may be dried. Thetemperature lower than the glass transition temperature of the polyamicacid herein may be 80° C. to 150° C. In this case, the product may havea low strength. For example, when the product is pressed by a nail, theshape of the product may be deformed.

The thermal imidization process of the polyamic acid according toembodiments may be performed at a temperature higher than the glasstransition temperature. Accordingly, the polyamic acid is cured so thata polyimide, as a final product, may have a high strength. The strengthof the final product, for example, may be the same or similar to thestrength of steel. Therefore, a grinding or a polishing process may beperformed on a film prepared from the polyimide. Applicability of apolyimide film may be improved.

The polyamic acid imidization process according to embodiments may beperformed by a chemical imidization process. The chemical imidizationprocess may include using a dehydration catalyst to remove waterincluded in the polyamic acid and heating the polyamic acid at a hightemperature thereafter. The dehydration catalyst may include aceticanhydride and/or pyridine. A polyimide may be prepared by the chemicalimidization process and the polyimide may have a high strength in asolid state. In the specification, unless otherwise defined, a hightemperature may refer to a temperature of 200° C. or more, specifically,about 200° C. to 350° C.

A polyimide may be prepared by heating a polyamic acid at a hightemperature (i.e. 200° C. to 350° C.). In general, the transmittance ofa polyimide may be decrease due to a high temperature heat. After thehigh temperature heating process, for example, the polyimide may be indark brown. This may be because during the high temperature heatingprocess, π electrons in the cyclic chain structure of the polyimide aretransferred to the resonance energy excitation band of theintermolecular bonds in the wavelength region of visible light due to acharge transfer complex phenomenon. the polyamic acid according toembodiments may include a high electronegative element/group.Accordingly, even if the polyamic acid is heated at a high temperature,π electron transfer may be decreasing and resonance may be reduced.

Hereinafter, an adhesive strength of an adhesive will be described.

When the adhesive includes organic materials such as an epoxy polymer,an acryl polymer and/or a polyimide, the adhesive strength of theadhesive may be described in four ways below.

Adhesive strength by electrostatic force: when an electric charge isgenerated on the surfaces of two subjects to be adhered, anelectrostatic force is applied between the surfaces of the two subjectslike a capacitor to have an adhesive strength. However, an adhesivestrength ratio by the electrostatic force to a total adhesive strengthmay be quite small.

Mechanical interlocking: when the surfaces of two subjects to be adheredare rough and have particularly fine pores, a solution adhesive may bepermeated into the pores and solidified. Accordingly, the two subjectsto be adhered may be mechanically interlocked. The mechanicalinterlocking may have a high adhesive strength. When increasing theroughness on the surfaces of the two subjects to be adhered by thesurface treatment process, the adhesive strength by the mechanicalinterlocking may increase.

Inter-diffusion: an adhesive strength by inter-diffusion is a kind ofmechanical interlocking. Polymer adhesive in solution is diffused andpermeated from the surface of a subject into an inner of the subject andthe polymer adhesive is solidified to generate the adhesive strength.When the surface of a subject to be adhered is smooth, the adhesivestrength by inter-diffusion may be generated.

Adsorption: adsorption is a most commonly applied adhesive mechanism.Primary forces may be generated by an ionic bond, a covalent bond and/ora metallic bond among atoms and molecules between two subjects to beadhered. In this case, the covalent bond of the primary force may be avalence covalent bond. Secondary forces may include van der Waals force,an atom/molecule covalent bond, an electric dipole bond, or an induceddipole bond, and/or bond from acid interaction. The covalent bond of thesecondary forces may be a covalent bond among atoms, molecules, orbetween an atom and a molecule. When the distance between the twosubjects to be adhered is 1 nm or more, the primary forces out of thetotal adsorption adhesive strength between the two subjects may not besignificant. In other words, when the distance between the two subjectsto be adhered is 1 nm or more, the adsorption adhesive strength betweenthe two subjects may be an adhesive strength by the secondary forces.The adhesive strength by a chemical bond may be mostly an adhesivestrength by the secondary forces.

When an adhesive includes organic materials such as an epoxy polymer,acryl polymer, and/or a polyimide, an adhesive strength byinter-diffusion from mechanical interlocking and/or an adhesive strengthby secondary forces may bond an adhesive to a subject to be adhered.

Hereinafter, types of a polyimide and polyimide adhesion based on a typewill be described.

A polyimide may be classified into a thermosetting polyimide and athermoplastic polyimide by their thermal properties.

(1) Thermosetting Polymer

In general, when a thermosetting polyimide is once cured, thethermosetting polyimide has non-processability. For example, the form ofthe cured thermosetting polyimide may hardly change. In this case,curing of the thermosetting polyimide may be performed at a temperaturehigher than the glass transition temperature. When the thermosettingpolyimide is cured, even if the temperature increases, the strength ofthe thermosetting polyimide may not change.

Adhesion of the thermosetting polyimide may be performed by using apolyamic acid solution or a polyimide film. For example, a polyamic acidsolution may be prepared. A polyamic acid layer may be formed by coatingthe surface of a subject to be adhered with the polyamic acid solution.The polyamic acid layer may be dried for 1-2 hours at a temperature of120° C. As another example, the polyimide layer after being dried may beprovided between the subjects to be adhered. After the drying process,the polyimide film may include 3-5 wt % of solvent. The solvent mayinclude volatile materials such as water. Pressure of 0.1-1 MPa may beapplied to the subjects to be adhered and the polyimide film. Applyingthe pressure may be performed for more than an hour at a temperature of300° C. under a nitrogen atmosphere. Accordingly, the polyimide film iscured and the subjects to be adhered may be bonded to the polyimidefilm. The principal element of an adhesive strength between thepolyimide film and the subjects to be adhered may be the adhesivestrength by inter-diffusion. The secondary element of the adhesivestrength between the polyimide film and the subjects to be adhered maybe the adhesive strength by a chemical bonding force. In this case, thesolvent in the polyimide film may be evaporated during the curingprocess. Accordingly, voids may be generated between the polyimide filmand the subjects or bubbles may be formed in the polyimide film. Theadhesive strength of the polyimide film may decrease due to the voidsand the bubbles. Also, the polyimide film may not be used for preparingflexible copper clad laminate due to the voids.

(2) Thermoplastic Polymer

When a cured thermoplastic polyimide is provided at a temperature higherthan the curing temperature, the strength of the thermoplastic polyimidemay decrease and the volume of the thermoplastic polyimide may expand.In addition, the cured thermoplastic polyimide may change into a flowingstate from a solid state at a certain temperature higher than the curingtemperature. Being in the flowing state may refer to a state in whichthe cured thermoplastic polyimide melts. For example, when thethermoplastic polyimide in the flowing state is compressed between twoplates, the thermoplastic polyimide may flow out of the sides of theplates.

Adhesion of the thermoplastic polyimide may be performed by using apolyamic acid solution or a polyimide film. For example, the adhesion ofthe thermoplastic polyimide may be performed after the form of thethermoplastic polyimide changes at a temperature higher than the curingtemperature of the thermoplastic polyimide or may be performedsimultaneously while the form changes.

(3) Adhesive According to Embodiments

A refractive index of an adhesive according to embodiments of theinventive concept may have nothing to do with a temperature condition.For example, even if the temperature changes, the refractive index ofthe adhesive may have a constant value. Moreover, refractive indexmatching conditions for subjects to be adhered may be satisfied.

The adhesive may have a high mechanical, chemical resistance, and a hightransmittance. A polyimide according to embodiments may be thermosettingor thermoplastic. A polyimide according to embodiments may include athermosetting polyimide, satisfy the refractive index-matchingconditions, and may have a high mechanical, chemical resistance, and ahigh transmittance. When a polyimide according to embodiments is athermoplastic polyimide, the thermoplastic polyimide may have asignificantly high glass transition temperature.

Grinding or polishing generally may not be performed on an adhesive madeof organic materials. This is because frictional heat is generated onthe surface during the grinding or polishing, resulting in putting thesurface in a flowing state. Since a polyimide according to embodimentsmay have a high strength at a temperature of 400° C. or higher,planarization may be carried out on an adhesive layer. Planarizationprocess may include grinding process or polishing process.

A broken link such as a dangling bond may be generated on the surface ofthe planarized polyimide layer. When a polyamic acid or a solvent isapplied to the surface of a polyimide layer, a dangling bond and apolyamic acid may be chemically re-bonded.

Bonding forces between an adhesive and subjects to be adhered accordingto embodiments may include bonding forces by secondary forces andbonding forces by inter-diffusion, the bonding forces by the secondaryforces may be stronger than the bonding forces by the inter-diffusion.An adhesive according to embodiments may have a stronger bonding forceand better adhesive surface conditions at a second temperature conditionthan at a first temperature condition. The first temperature conditionis the curing temperature of a thermosetting polyimide which is about300° C. to about 350° C. The second temperature condition is a chemicalreaction temperature which is about 80° C. to about 150° C.

Hereinafter, an adhesive structure, a method for preparing an adhesivestructure, and a method for preparing an optical module according toembodiments of the inventive concept will be described. Duplicatecontent described above will be omitted.

FIGS. 1 to 11 show drawings to describe a method for preparing anoptical module according to an embodiment. Hereinafter, duplicatecontent described above will be omitted.

Referring to FIG. 1, a substrate structure 100 may be prepared. Thesubstrate structure 100 may include a substrate 110, a lower clad layer120, an optical waveguide layer 130, and an upper clad layer 140 whichare stacked. The substrate 110 may include a semiconductor material suchas crystalline silicon. The substrate 110 may be a semiconductor wafer.The substrate 110, for example, may have a refractive index of about3.45. The substrate 110 may have a first region R1 and a second regionsR2 as viewed in a plain view. The first region R1 may be providedbetween the second regions R2.

The lower clad layer 120 may include a semiconductor oxide such as asilicon dioxide. The lower clad layer 120, for example, may have arefractive index of about 1.45. The lower clad layer 120 may be formedby a thermal oxidation process.

The optical waveguide layer 130 may be provided on the lower clad layer120. The lower clad layer 120 may have a lower refractive index than theoptical waveguide layer 130. The optical waveguide layer 130 may have alower refractive index than the substrate 110. The optical waveguidelayer 130 may include silicon nitride or silicon oxynitride. The siliconnitride may have a refractive index of about 2.0. The silicon oxynitridemay have a refractive index of about 1.45-2.0. The optical waveguidelayer 130 may have a refractive index of about 1.5-2.0.

The upper clad layer 140 may cover a portion of the upper surface of theoptical waveguide layer 130. The upper clad layer 140, for example, mayexpose at least a portion of the upper surface of the optical waveguidelayer 130 on the second regions R2 of the substrate 110 while coveringthe upper surface of the optical waveguide layer 130 on the first regionR1 of the substrate 110.

The upper clad layer 140 may have a lower refractive index than theoptical waveguide layer 130. The upper clad layer 140 may includesemiconductor oxides such as a silicon dioxide. The upper clad layer 140may have a refractive index of about 1.45. The upper clad layer 140 maybe formed by a deposition process such as plasma vapor deposition.

Referring to FIG. 2, an adhesive may be prepared. The adhesive mayinclude the polyamic acid solution described above. The adhesive, forexample, may include a polyamic acid and a solvent. The solvent may bethe residual solvent described in the embodiment of preparing a polyamicacid solution. The solvent may include NMP (N-methyl-1-2-pyrollidone).As another example, the solvent may include DMAc (N,N-dimethylacetamide,DMF (dimethylforamide), and/or m-cresol. The characteristics of theadhesive are as described above.

A first adhesive layer 211 may be formed on the substrate structure 100by using the adhesive. Forming the first adhesive layer 211 may includespin-coating the substrate structure 100 with the adhesive to form firstpreliminary adhesive layers and curing the first preliminary adhesivelayers. The first preliminary adhesive layers may cover the opticalwaveguide layer 130 and the upper clad layer 140. The first preliminaryadhesive layers may be formed with a thickness of about 1 μm to about 2μm. The first preliminary adhesive layers may include a polyamic acid.The first adhesive layer 211 may be formed by performing a curingprocess on the first preliminary adhesive layers. The first adhesivelayer 211 may include a polyimide. In other words, the polyamic acid maybe cured to form the polyimide. The curing process may include a firstprocess performed at a first temperature, a second process performed ata second temperature, and a third process performed at a thirdtemperature. The first, second, and third process may be performedconsecutively. The second temperature may be higher than the firsttemperature, and the third temperature may be higher than the secondtemperature. For example, the first temperature may be 120° C., thesecond temperature may be 250° C., and the third temperature may be 400°C. The rate of temperature increase may be 3-5° C./min. Each of thefirst, second, and third process may be performed for about 60 minutes.The curing process, as an example, may be performed in an oven of anitrogen atmosphere. As another example, the curing process may beperformed on an atmospheric hot plate. After the third process, thefirst adhesive layer 211 may be provided at room temperature (about 25°C.). In this case, the rate of temperature drop may be 5-8° C./min.

The first adhesive layer 211 may conformally cover the upper and sidesurfaces of the upper clad layer 140 and the exposed upper surface ofthe optical waveguide layer 130.

Referring to FIG. 3, second adhesive layers 212 may be formed on thefirst adhesive layer 211 to form an adhesive layer 210. According toembodiments, a mask pattern 900 may be formed on the first adhesivelayer 211 before the second adhesive layers 212 are formed. The maskpattern 900 may expose the first adhesive layer 211 on the secondregions R2 of the substrate 110 while covering the first adhesive layer211 on the first region R1 of the substrate 110. The mask pattern 900may include a photoresist material. For example, the photoresistmaterial may include a negative photoresist material.

Forming the second adhesive layer 212 may include spin-coating the firstadhesive layer 211 exposed by the mask pattern 900 with the adhesive toform second preliminary adhesive layers and curing the secondpreliminary adhesive layers. The adhesive may include the same polyamicacid solution as the adhesive used for forming the first adhesive layer211. The second preliminary adhesive layers may include a polyamic acid.The spin-coating process may be repeated a plurality of times and eachof the second preliminary adhesive layers may include a plurality ofstacked layers. The spin-coating process may be performed till thesecond preliminary adhesive layers have a thickness of about 5 μm toabout 15 μm.

The second preliminary adhesive layers may be cured to form secondadhesive layers 212. Curing the second preliminary adhesive layers maybe performed in the same way of curing the first preliminary adhesivelayers described in FIG. 2. For example, the curing process may includea first process performed at a first temperature, a second processperformed at a second temperature, and a third process performed at athird temperature. The first, second, and third process may be performedconsecutively. The second temperature may be higher than the firsttemperature, and the third temperature may be higher than the secondtemperature. For example, the first temperature may be 120° C., thesecond temperature may be 250° C., and the third temperature may be 400°C. After the third process, the first adhesive layer 211 may be providedat room temperature (about 25° C.). A first drying process of the secondpreliminary adhesive layers and a removal process of the mask pattern900 may be performed after the second process and before the thirdprocess. The removal process of the mask pattern 900 may be carried outby using a photoresist remover. The removal process of the mask pattern900 may expose the first adhesive layer 211 on the first region R1 ofthe substrate 110. The sequence of the removal process of the maskpattern 900 may be variously modified. The polyamic acid may be cured bythe curing process to form a polyimide. Therefore, the second adhesivelayers 212 may include the polyimide. Specifically, the second adhesivelayers 212 may include the same polyimide as the first adhesive layer211. For example, the chemical structure and composition ratio of thepolyimide of each of the second adhesive layers 212 may be same as thechemical structure and composition ratio of the polyimide of the firstadhesive layer 211, respectively. Hereinafter, the “same polyimide” inthe specification may indicate the polyimide substantially having thesame chemical structure and composition ratio. The second adhesivelayers 212 may be spaced apart from each other. The second adhesivelayers 212 may be formed on the second regions R2 of the substrate 110and cover the first adhesive layer 211.

The adhesive layer 210 may be prepared based on the embodimentsdescribed so far. The adhesive layer 210 may include the first adhesivelayer 211 and the second adhesive layers 212 on the first adhesive layer211. Although FIG. 3, FIG. 4, FIGS. 10 to 12, FIG. 13A, and FIG. 13Bseparately illustrate the first adhesive layer 211 and the secondadhesive layers 212 for convenience of description, the interfacebetween the first adhesive layer 211 and the second adhesive layers 212may not be distinguished.

Referring to FIG. 4, a planarization process may be performed on thesecond adhesive layers 212 to form active functional groups. Theplanarization process may decrease the thickness of the second adhesivelayers 212. The planarization process may include at least one ofgrinding and polishing processes. For example, the planarization processmay include performing the grinding process till the second adhesivelayer 212 has a thickness of about 3 μm to about 7 μm and thenperforming the polishing process till each of the second adhesive layer212 has a thickness of about 1 μm to about 5 μm. As another example, theplanarization process may include a chemical mechanical planarization(CMP) process. The planarization process, as another example, may beperformed as the grinding process alone, or as the polishing processalone. The planarization may be confirmed by observing the reflectionand transmission of light irradiated on the second adhesive layers 212.

Bonding in the polyimide molecules of the second adhesive layers 212 maybe broken by the planarization process. Accordingly, the activefunctional groups may be formed on planarized upper surfaces 212 a ofthe second adhesive layers 212. The active functional groups may includedangling bonds or radicals.

According to embodiments, as the first adhesive layer 211 is formed, theupper clad layer 140 and the optical waveguide layer 130 may beprevented from damaged from the planarization process of the secondadhesive layers 212.

Referring to FIG. 5, an adhesive is applied to a first temporarysubstrate 810 to form a third preliminary adhesive layer 233. The firsttemporary substrate 810, for example, may include a slide glass. Theadhesive may be the same as the polyamic acid solution described above.In other words, the third preliminary adhesive layer 233 may include thepolyamic acid solution. The third preliminary adhesive layer 233 mayhave a thickness of about 1 to about 10 μm.

A prism 300 may be prepared. The prism 300 may have a first surface 300b and an inclined surface 300 a. The first surface 300 b of the prism300 may be a lower surface of the prism 300. The angle θ1 between thefirst surface 300 b and the inclined surface 300 a of the prism 300 maybe an acute angle. The prism 300 may include crystalline silicon orgallium phosphide (GaP). The gallium phosphide may have a refractiveindex of about 3.16. The prism 300 may have a greater refractive indexthan that of the optical waveguide layer 130 described in FIG. 1.Specifically, the prism 300 may have a greater refractive index thanthat of the core of the optical waveguide.

The prism 300 may be provided on the first temporary substrate 810 suchthat the first surface 300 b of the prism 300 contacts the thirdpreliminary adhesive layer 233.

Referring to FIG. 6, since the third preliminary adhesive layer 233 isin a solution state, at least some portion of the third preliminaryadhesive layer 233 may cover the first surface 300 b of the prism 300.The prism 300 may be separated from the first temporary substrate 810.The at least some portion of the third preliminary adhesive layer 233may be separated from the first temporary substrate 810 along with theprism 300 to form a fourth preliminary adhesive layer 234. The fourthpreliminary adhesive layer 234 may cover the first surface 300 b of theprism 300. Another portion of the third preliminary adhesive layer 233may remain on the first temporary substrate 810.

Referring to FIG. 7, a second temporary substrate 820 may be prepared.The second temporary substrate 820 may be, for example, a slide glass.The second temporary substrate 820 may be a substrate on which apolyamic acid is not applied.

The prism 300 may be provided on the second temporary substrate 820 suchthat the fourth preliminary adhesive layer 234 contacts an upper surfaceof the second temporary substrate 820. The prism 300 may be moved in adirection parallel to the upper surface of the second temporarysubstrate 820 while the fourth preliminary adhesive layer 234 is incontact with the upper surface of the second temporary substrate 820.Moving the prism 300 may be repeated one to three times. Accordingly,some of the fourth preliminary adhesive layer 234 remains on the uppersurface of the second temporary substrate 820, so that the thickness ofthe fourth preliminary adhesive layer 234 on the first surface 300 b ofthe prism 300 may decrease. For example, the fourth preliminary adhesivelayer 234 may have a thickness of 0.001 μm to less than 1 μm. The firstsurface 300 b of the fourth preliminary adhesive layer 234 may befurther flattened by the contact with the second temporary substrate820.

Referring to FIG. 8, the prism 300 may be turned upside down so that thefourth preliminary adhesive layer 234 faces upward. The curing processmay be performed on the fourth preliminary adhesive layer 234 to form aprism adhesive layer 230. The curing process of the fourth preliminaryadhesive layer 234 may be performed in the same way of curing the firstpreliminary adhesive layer of FIG. 2. For example, the curing process ofthe fourth preliminary adhesive layer 234 may include a first processperformed at a first temperature, a second process performed at a secondtemperature, and a third process performed at a third temperature. Thefirst, second, and third processes may be performed consecutively. Thesecond temperature may be higher than the first temperature and thethird temperature may be higher than the second temperature. Forexample, the first temperature may be 120° C., the second temperaturemay be 250° C., and the third temperature may be 400° C. After the thirdprocess, the first adhesive layer 211 may be provided at roomtemperature (about 25° C.). The polyamic acid in the fourth preliminaryadhesive layer 234 may be cured by the curing process to form a prismadhesive layer 230 including a polyimide. The prism adhesive layer 230may cover the first surface 300 b of the prism 300 and have a thicknessof 0.001 μm to less than 1 μm. The prism adhesive layer 230 may includea polyimide. The polyimide included in the prism adhesive layer 230 maybe the same as the polyimide included in the first adhesive layer 211and the second adhesive layers 212 described in FIG. 4.

Referring to FIG. 9, a polyamic acid layer 220 may be formed on at leastone of the prism adhesive layer 230 and the second adhesive layers 212.For example, the polyamic acid layer 220 may be formed to cover theprism adhesive layer 230. The polyamic acid layer 220 may be formed by acoating process using the adhesive from the inventive concept. As thespeed of the coating process increases, the thickness of the polyamicacid layer 220 may decrease. According to embodiments, the coatingprocess may be carried out for 60 seconds at a high rotational rate. Thecoating process may be performed at a very high speed so that thepolyamic acid layer 220 may be formed thin in thickness.

Referring to FIGS. 10 and 11, the substrate structure 100 on which thefirst adhesive layer 211 and the second adhesive layers 212 are formedmay be prepared, and the prism 300 on which the prism adhesive layer 230and the polyamic acid layer 220 are formed may be prepared. Thesubstrate structure 100, the first adhesive layer 211, and the secondadhesive layers 212 may be the same as those described in FIGS. 1 to 4.The prism adhesive layer 230 may be formed as shown in FIGS. 5 to 8, andthe polyamic acid layer 220 may be prepared as shown in FIG. 9.

According to embodiments, the prism 300 may be provided in one pair, andthe prism adhesive layers 230 may be provided on the first surfaces 300b of the prisms 300, respectively. The prisms 300 may be disposed atpositions vertically overlapping with the corresponding second adhesivelayers 212. The number of the prisms 300 and the number of the secondadhesive layers 212 are not limited as shown. Hereinafter, a singleprism 300, a single prism adhesive layer 230, and a single secondadhesive layer 212 will be described in the following description ofFIGS. 10 and 11 for simplicity.

The prism 300 may be disposed on the substrate structure 100 such thatthe prism adhesive layers 230 face the corresponding second adhesivelayers 212. In this case, the polyamic acid layer 220 may be interposedbetween the prism adhesive layer 230 and the second adhesive layer 212.The polyamic acid layer 220 may be in physical contact with the uppersurface of the second adhesive layer 212. Specifically, the polyamicacid layer 220 may contact the active functional groups on the uppersurface 212 a of the second adhesive layer 212. The polyamic acid layer220 may include a polyamic acid solution and may be in a liquid state.

Bonding the adhesive layer 210 to the prism adhesive layer 230 may beperformed by applying pressure on the prism 300 and the substratestructure 100. As the time between contacting the polyamic acid layer220 with the upper surface of the second adhesive layer 212 and applyingpressure decreases, the material of the polyamic acid layer 220 mayprevent from permeating into the prism adhesive layer 230 or the secondadhesive layer 212. According to embodiments, right after the polyamicacid layer 220 is in contact, pressure may be applied to the prism 300and the substrate structure 100. Accordingly, excessive permeation ofthe material of the polyamic acid layer 220 into the prism adhesivelayer 230 or the second adhesive layer 212 may be prevented.

Applying pressure may be performed for 10 minutes to 60 minutes at 1 MPato 10 MPa. As a pressure of 10 MPa or less is applied, physical damageof the first adhesive layer 211, the second adhesive layer 212, or theprism adhesive layer 230 may be prevented. The physical damage mayinclude fracture. By applying the pressure, secondary forces may beformed among the active functional groups of the prism adhesive layer230, the polyamic acid layer 220, and the second adhesive layer 212. Theprism adhesive layer 230 may be bonded to the second adhesive layer 212by the secondary forces. That is, bonding the prism adhesive layer 230to the adhesive layer 210 may include forming intermolecular van derWaals forces, an electric dipole bond and/or an induced dipole bondamong a polyamic acid included in the polyamic acid layer 220 and thepolyimide molecule included in the prism adhesive layer 230, and theactive functional groups.

As another example, the active functional groups of the polyamic acid,the prism adhesive layer 230, and the second adhesive layer 212 includedin the polyamic acid layer 220 may be chemically reacted by applyingpressure. Accordingly, the prism adhesive layer 230 may be bonded to theadhesive layer 210. In this case, bonding the prism adhesive layer 230to the adhesive layer 210 may include forming ionic, covalent, and/ormetal bonds between the polyamic acid layer 220, the polyimide moleculesof the prism adhesive layer 230, and the active functional groups.

Some of the polyamic acid layer 220 may be used to form adhesion betweenthe prism adhesive layer 230 and the second adhesive layer 212. Thepolyamic acid layer 220 may include the same material (e.g. the samepolyamic acid) as the adhesive used in preparing the second adhesivelayers 212 and the adhesive used in preparing the prism adhesive layer230. Accordingly, re-bonding between the active functional group of thesecond adhesive layer 212 and the polyamic acid included in the polyamicacid layer 220, and the bonding between the active functional group ofthe adhesive layer 212 and the prism adhesive layer 230 may be wellformed.

Since the polyamic acid layer 220 is in a liquid state, most of thepolyamic acid layer 220 may be released to the side of the prism 300 byapplying the pressure. The portion of the released polyamic acid layer220 may be a portion that is not used to form a bond between the prismadhesive layer 230 and the active functional group of the secondadhesive layer 212. The released polyamic acid layer 220 may be removed.Accordingly, after the adhesion between the prism adhesive layer 230 andthe second adhesive layer 212 is completed as shown in FIG. 11, thepolyamic acid layer 220 may not remain between the prism adhesive layer230 and the second adhesive layer 212.

The prism adhesive layer 230 may be bonded to the adhesive layer 210 toform an adhesive structure 200. The adhesive structure 200 may beinterposed between the prism 300 and the substrate structure 100. Theadhesive structure 200 may include the first adhesive layer 211, thesecond adhesive layer 212 and the prism adhesive layer 230, and theprism adhesive layer 230 may be in a state bonded to the second adhesivelayer 212.

When applying pressure is performed at a temperature of less than 80°C., it may be difficult to sufficiently generate the secondary bondingforce of the polyamic acid layer 220, the prism adhesive layer 230 andthe second adhesive layer 212. When an adhesive force between the prismadhesive layer 230 and the second adhesive layer 212 is formed at thecuring temperature (e.g. 200-350° C.) of the polyamic acid layer 220,voids or bubbles may be generated in the polyamic acid layer 220.According to embodiments, the applying of the pressure may be performedat a temperature of 80-150° C. In detail, applying pressure may beperformed at a temperature of 120° C. Accordingly, the formation ofvoids or bubbles between the second adhesive layer 212 and the prismadhesive layer 230 may be prevented. Bonding forces between the secondadhesive layer 212 and the prism adhesive layer 230 may be improved. Inthe most sophisticated way, the polyamic acid layer 220 is fullyreleased to the side while applying pressure, and when the secondadhesive layer 212 and the prism adhesive layer 230 are bonded togetherby the secondary forces at a temperature of 120° C., not only voids orbubbles may not be formed but also a favorable bonding force may beexhibited.

According to embodiments, as the first adhesive layer 211 is provided, acontact area between the adhesive structure 200 and the substratestructure 100 may increase. Accordingly, the second adhesive layers 212may be more firmly bonded to the substrate structure 100.

An optical module 1 may be prepared by the manufacturing exampledescribed above. The optical module 1 may include the substratestructure 100, the adhesive structure 200, and the prism 300.

FIG. 12 is a drawing illustrating a method of forming an adhesivestructure and an optical module according to other embodiments.Duplicate content as described above will be omitted.

Referring to FIG. 12, polyamic acid layers 220 may be formed on theupper surfaces of the second adhesive layers 212, respectively. Themethod and material for forming the polyamic acid layers 220 are thesame as those described above in FIG. 9. The polyamic acid layers 220may be in physical contact with the upper surfaces of the secondadhesive layers 212, respectively. Specifically, the polyamic acidlayers 220 may contact the active functional groups on the uppersurfaces 212 a of the second adhesive layers 212. Each of the polyamicacid layers 220 may include a polyamic acid solution and be in a liquidstate.

Referring back to FIG. 10, the prism 300 having the prism adhesive layer230 may be prepared. For example, the prism adhesive layer 230 may beprepared as shown in FIGS. 4 to 8, and the polyamic acid layer 220described in FIG. may not be formed on the lower surface of the prismadhesive layer 230. The prism 300 on which the prism adhesive layer 230is formed may be prepared in one pair.

The prisms 300 may be disposed on the substrate structure 100 such thatthe prism adhesive layers 230 face the second adhesive layers 212,respectively. The polyamic acid layers 220 may be interposed between theprism adhesive layers 230 and the second adhesive layers 212,respectively.

As another example, the prism 300 having the polyamic acid layer 220 andthe prism adhesive layer 230 shown in FIG. 9 may be prepared. The prism300 may be prepared in plurality. The prisms 300 may be disposed on thesubstrate structure 100 such that the polyamic acid layers 220 on thefirst surfaces 300 b of the prisms 300 are in contact with the polyamicacid layers 220 on the upper surface of the substrate structure 100 ofFIG. 12, respectively.

Referring to FIG. 11, pressure may be applied to the prisms 300 and thesubstrate structure 100 under the same conditions as described above toform the adhesive structure 200. The prisms 300 may be bonded to thesubstrate structure 100 through the adhesive structure 200. The opticalmodule 1 may be prepared by the manufacturing example described above.

FIG. 13A is a cross-sectional view illustrating an optical moduleaccording to other embodiments. FIG. 13B is an enlarged view of region Aof FIG. 13A. Duplicate content as described above will be omitted.

FIGS. 13A and 13B, the optical module 2 may include the substratestructure 100, the adhesive structure 200, the prisms 300, an opticaldevice 400, and a photodetector device 500. The substrate structure 100may include the substrate 110, the lower clad layer 120, the opticalwaveguide layer 130, and the upper clad layer 140 which are stacked. Theadhesive structure 200 may include the adhesive layer 210 and the prismadhesive layers 230, and the adhesive layer 210 may include the firstadhesive layer 211 and the second adhesive layers 212. The prisms 300may include a first prism 301 and a second prism 302 spaced apart fromeach other.

The optical element 400 may be disposed on the first prism 301. Theoptical device 400 may include a light generating unit 410, a lens 420,an adhesive pattern 430, and a light transmitting unit 440. The lightgenerating unit 410 may generate and emit the laser light L. The lightgenerating unit 410 may be a vertical cavity surface emitting laser(VCSEL) or a laser diode. As shown in FIG. 13B, the laser light Lemitted from the light generating unit 410 may have a second angle θ2 asa radiation angle. For example, the second angle θ2 may be 20 to 40degrees. The light generator unit 410 may include an opening 411, andthe laser light L may be emitted from the opening 411.

The lens 420 may be provided on a lower surface of the light generatingunit 410. The lens 420 may include a base portion 421 and a protrusion422. The base portion 421 may have the form of a flat plate. Theprotrusion 422 may have the form of a hemisphere. The base portion 421may be provided on the light generating unit 410, and the protrusion 422may protrude from the base portion 421 toward the prism 300. The lens420 may have a refractive index of 1.65 to 2.5. The lens 420 may includeat least one of SiC, GaN, Si₃N₄, TiN, LiNbO₃, TiO₂, ZnSe, and Polyimide.

The adhesive pattern 430 may be provided on the lower surface of thelens 420. The adhesive pattern 430 may cover the lens 420. In otherwords, the adhesive pattern 430 may cover the lower surface of the baseportion 421 of the lens 420 and the lower surface of the protrusion 422of the lens 420. The adhesive pattern 430 may have a refractive index of1.3 to 1.55. The adhesive pattern 430 may include an optical adhesive.

The light transmitting unit 440 may be provided on the lower surface ofthe adhesive pattern 430. The light transmitting unit 440 may includeglass or quarts. The light transmitting unit 440 is illustrated as beingspaced apart from the protrusion 422 of the lens 420 by the adhesivepattern 430, but may not be limited thereto. For example, the lighttransmitting unit 440 may be in contact with the protrusion 422 of thelens 420.

For the operation of the optical module 2 according to an embodiment ofthe inventive concept, as shown in FIG. 13B, the laser light L generatedby the light generating unit 410 of the optical device 400 may passthrough the lens 420 and the adhesive pattern 430. While passing throughthe lens 420 and the adhesive pattern 430, the radiation angle of thelaser light L may be reduced. Accordingly, the laser light L passingthrough the light transmitting unit 440 may be parallel light. In otherwords, the radiation angle of the laser light L passing through thelight transmitting unit 440 may be 0 degrees.

The laser light L that has passed through the light transmitting unit440 may be vertically incident to the inclined surface 300 a of theprism 300 to pass through the prism 300. The laser light L passingthrough the prism 300 may form a third angle θ3 with the first surface300 b of the prism 300. The third angle θ3 may correspond to theinclination angle of the prism 300. In other words, the sum of the firstangle θ1 and the third angle θ3 may be 90 degrees.

The laser light L that has passed through the prism 300 may pass throughthe adhesive structure 200 and be incident to the optical waveguidelayer 130. The laser light L incident to the optical waveguide layer 130may be reflected by the lower clad layer 120 and the upper clad layer140, and may travel along the optical waveguide layer 130.

If the light passing through the light transmitting unit 440 of theoptical device 400 is not parallel light, the laser light L may not passthrough the prism 300 and the adhesive structure 200 to be focused onthe optical waveguide layer 130. For example, when the radiation angleof the laser light L passing through the light transmitting unit 440 is2 degrees or more, a substantial portion of the laser light L may not befocused on the optical waveguide layer 130. According to the inventiveconcept, the laser light L emitted from the optical device 400 may beparallel light, so that the laser light L may be focused on the opticalwaveguide layer 130.

As shown in FIG. 13A, a first wavelength light may be emitted from theoptical device 400. The first wavelength light may be the laser light Ldescribed in FIG. 13B. The first wavelength light may pass through theadhesive structure 200 and be incident to the optical waveguide layer130, and may travel in the optical waveguide layer 130. The firstwavelength light may be transmitted below the second prism 302 throughthe optical waveguide layer 130. The first wavelength light may passthrough the second prism 302. The photodetector device 500 may beprovided on the second prism 302. The light passing through the secondprism 302 may be transmitted to the photodetector device 500. Thephotodetector device 500 may detect the first wavelength light.

Although not shown, a first filter may be further provided between theadhesive structure 200 and the first prism 301. The first filter maytransmit the first wavelength light. The first filter may not transmitlight having a wavelength different from the first wavelength. A secondfilter may be further provided between the adhesive structure 200 andthe photodetector device 500. The second filter may transmit the firstwavelength light. The second filter may not transmit light having awavelength different from the first wavelength.

Hereinafter, with reference to a comparative example and an experimentalexample of the inventive concept, the preparation and evaluation resultsof the adhesive structure and the preparation and evaluation results ofthe optical module including the adhesive structure will be described.

1. Comparative Example

As described above, a substrate structure, an adhesive structure, and aprism are prepared. However, applying pressure to the substratestructure and the prism is performed at 300-400° C. Thereafter, anoptical device is placed on the prism. Current is applied to the opticaldevice to generate light in the optical device. The light output fromthe lower surface of the substrate structure is observed.

2. Experimental Example

As described above, a substrate structure, an adhesive structure, and aprism are prepared. Applying pressure to the substrate structure andprism is performed at 120° C. Thereafter, an optical device is placed onthe prism. Current is applied to the optical device to generate light inthe optical device. The light output from the lower surface of thesubstrate structure is observed.

Table 1 shows the measurement results of the material and the electricalconductivity contained in the film of comparative examples andexperimental examples.

TABLE 1 Voids or Bubbles Optical signal connection success rateComparative — Low Example Experimental — High Example

Referring to Table 1, the experimental example was observed to have ahigher optical signal connection success rate than the comparativeexample. It was observed that voids and bubbles were not generated inthe adhesive structure of the experimental example.

As described above, according to the present disclosure, an adhesivestructure may have improved adhesive strength, high-transparency, a highglass transition temperature, and solvent resistance. The adhesivestructure may be readily applied to a process for manufacturing asemiconductor device or an optical module

The foregoing detailed description is not intended to limit theinventive concept to the disclosed embodiments, and may be used invarious other combinations, modifications, and environments withoutdeparting from the spirit of the inventive concept. The attached claimsshould be construed to include other embodiments.

What is claimed is:
 1. A method for manufacturing an optical module, themethod comprising: preparing a substrate structure; applying a polyamicacid solution to an upper surface of the substrate structure to form anadhesive layer; performing a planarization process on an upper surfaceof the adhesive layer to form an active functional group on the uppersurface of the adhesive layer; applying a polyamic acid to a firstsurface of a prism to form a prism adhesive layer; forming a polyamicacid layer on at least one of the planarized upper surface of theadhesive layer and a lower surface of the prism adhesive layer, whereinthe polyamic acid layer is in a liquid state; disposing the prism on thesubstrate structure such that the polyamic acid layer contacts theadhesive layer and the prism adhesive layer; and bonding the prismadhesive layer to the adhesive layer by applying pressure to the prismand the substrate structure.
 2. The method of claim 1, wherein theapplying of pressure to the prism and the substrate structure isperformed at a temperature lower than a curing temperature of thepolyamic acid layer.
 3. The method of claim 2, wherein the applying ofpressure to the prism and the substrate structure is performed at atemperature ranging from 80° C. to 150° C.
 4. The method of claim 1,wherein the prism adhesive layer contains the same polyimide as theadhesive layer.
 5. The method of claim 1, wherein the polyamic acidlayer contains the same material as the polyamic acid solution.
 6. Themethod of claim 1, wherein the bonding of the prism adhesive layer tothe adhesive layer comprises forming intermolecular van der Waals force,an electric dipole bond or an induced dipole bond among a polyamic acidincluded in the polyamic acid layer, polyimide molecules included in theprism adhesive layer and the active functional group.
 7. The method ofclaim 1, wherein the active functional group comprises a dangling bond.8. The method of claim 1, wherein the bonding of the prism adhesivelayer to the adhesive layer comprises forming an ionic bond, a covalentbond or a metallic bond among a polyamic acid included in the polyamicacid layer, polyimide molecules included in the prism adhesive layer andthe active functional group.
 9. The method of claim 1, wherein thebonding of the prism adhesive layer to the adhesive layer comprises:permeating a polyamic acid included in the polyamic acid layer into theadhesive layer or the prism adhesive layer; and solidifying thepermeated polyamic acid.
 10. The method of claim 1, wherein: thesubstrate structure comprises an optical waveguide; the opticalwaveguide has a refractive index of 1.5 to 20; and the prism has agreater refractive index than the optical waveguide.
 11. The method ofclaim 1, wherein the forming of the adhesive layer comprises:spin-coating the polyamic acid solution on a surface of the substratestructure to form a first preliminary adhesive layer; conducting curingprocess on the first preliminary adhesive layer to form a first adhesivelayer, wherein the first adhesive layer includes a polyimide.
 12. Themethod of claim 11, wherein the forming of the adhesive layer comprises:forming a second preliminary adhesive layer on the first adhesive layer;and carrying out curing process on the second preliminary adhesive layerto form a second adhesive layer, wherein the second preliminary adhesivelayer includes a polyamic acid, and the second adhesive layer includes apolyimide.
 13. The method of claim 1, wherein the preparing of thesubstrate structure comprises stacking a lower clad layer, an opticalwaveguide, and an upper clad layer on a substrate.
 14. An optical modulecomprising: a substrate structure including a substrate, a lower cladlayer, an optical waveguide layer, and an upper clad layer which arestacked; a prism having a first surface and an inclined surface; and anadhesive structure provided between the substrate structure and thefirst surface of the prism and having a refractive index of 1.55 to2.00, wherein the adhesive structure includes: an adhesive layerprovided on the optical waveguide layer and the upper clad layer andincluding a polyimide; and a prism adhesive layer provided on the firstsurface of the prism and including the same polyimide as the adhesivelayer, wherein at least one of chemical bond and intermolecularinteraction is formed between the adhesive layer and the prism adhesivelayer.
 15. The optical module of claim 14, wherein the polyimidecomprises at least one among trifluoromethyl (—CF₃), sulfone (—SO₂)and/or ether (—O—) groups.
 16. The optical module of claim 14, whereinthe optical waveguide layer has a refractive index of 1.5 to 2.0 and theprism has a greater refractive index than the optical waveguide layer.17. The optical module of claim 14, wherein the adhesive structurecomprises: a polymerization unit derived from an aromatic dianhydridemonomer; and a polymerization unit derived from a monomer includingdiamine group.
 18. The optical module of claim 14, wherein transmittanceof the adhesive structure with a thickness of 1 μm regarding to lighthaving 500 nm to 2000 nm ranges from 95% to 100%.
 19. The optical moduleof claim 14, wherein the intermolecular interaction comprises van derWaals force, an electric dipole bond, or an induced dipole bond, andwherein the chemical bond comprises an ionic bond, a covalent bond or ametallic bond.
 20. The optical module of claim 14, wherein voids andbubbles are not formed between the adhesive layer and the prism adhesivelayer.